SbGA2oxC GENE-EXPRESSION REGULATION BY ABA SIGNALLING ELEMENTS

CANTORO R; AUGE GA; MUT P; BENECH-ARNOLD RB; RODRIGUEZ MV

Costa do Sauipe

Conferencia; 10th Conference of the International Society for Seed Science; 2011

ISSS (International Society for Seed Science)

Gibberellin levels are highly associated with the pre-harvest sprouting (PHS) response of two grain sorghum lines, IS9530 and RedlandB2 (Perez-Flores et al., 2003). IS9530 line shows high dormancy at maturity and this is in accordance with high SbGA2oxC gene (coding putative GA inactivation enzyme) expression during grain incubation (Rodriguez MV,unplubished data). Also, GA34 (catabolite) levels correlated negatively with GA4 accumulation in grains of both lines, further supporting that inactivation is a key process in determining active GA content in the embryo. Promoter sequences of this gene contain several cis-regulatory elements involved in ABA signalling regulation (ABREs). In addition, SbABI5 gene expression and protein abundance followed a similar accumulation pattern to the gene mentioned above, indicating that a possible interaction between SbGA2oxC gene promoter and ABI5 protein may occur (Rodriguez et al., 2009). Therefore, it is of interest to study the factors regulating SbGA2oxC gene expression, since it could be an important control point to regulate PHS in sorghum crops. A 1056 bp fragment of SbGA2oxC promoter upstream the initiation codon was cloned and sequenced for both sorghum lines. Sequences differed in three bases at positions -294, -521 and -770, one of which (at -294 position) resulted in the appearance of a new binding site for WRKY transcription factors in IS9530 (some of them reported to be involved in GA signalling response) (Rushton et al., 2010). To study possible interactions between ABI5 protein and SbGA2oxC promoter, recombinant ABI5 was overexpressed in bacteria and purified. EMSA studies are being carried out to test binding to the SbGA2oxC promoter. Preliminary results indicate that ABI5 binds in vitro to the 5´ end of the cloned SbGA2oxC promoter. In addition, in order to identify new transcription factors involved in SbGA2oxC gene expression regulation, fragments of the cloned promotor are being used as probe to catch, through SouthWestern Blot technique, interacting partners present in embryo nuclear-enriched protein extracts. In cropping systems, non-homogeneous germination can result in reduced yield and elevated operational costs because of non-uniform crop development, and PHS during grain maturation can cause low quality in final product. A deeper understanding of GA and ABA signalling interaction during grain sorghum germination would be a useful tool to manipulate PHS occurrence in sorghum crops.